The present invention relates generally to a fiber optic cable and an associated fabrication method and apparatus and, more particularly, to a fiber optic cable having a slotted core and an associated fabrication method and apparatus.
One common fiber optic cable design includes a slotted cable core in which the outer surface of the cable core defines a number of lengthwise extending slots. Typically, the slots have a helical lay configuration, although the slots can have other configurations such as an S-Z stranded lay configuration or a linear configuration. The slotted cable core is typically formed around a center strength member which, in turn, is commonly formed of a plurality of stranded steel strength members, a single steel rod, or a glass or aramid fiber reinforced plastic member that imparts strength to the fiber optic cable and resists buckling. A fiber optic cable having a slotted cable core also includes a plurality of optical fibers disposed within the slots and a protective jacket that surrounds the cable core and the optical fibers, thereby protecting the optical fibers.
Fiber optic cables having slotted cable cores are typically formed by extruding the slotted cable core over the central strength member. In this regard, the central strength member typically passes through an extruder and a molten material, such as a molten thermoplastic material, is extruded under pressure about the central strength member. The central strength member and the surrounding thermoplastic material emerge from the extruder through a die opening. The shape of the die opening defines the shape of the outer surface of the thermoplastic material extruded over the central strength member. For example, the die opening can include a number of inwardly extending teeth or projections that define respective slots in the cable core.
As the thermoplastic material cools, the thermoplastic material hardens into a final shape. During the cooling process, the extruded thermoplastic material may become somewhat deformed due to the effects of gravity upon the soft mass of thermoplastic material. This deformation is termed slumping. In order to limit the adverse effects of slumping, the cable core can be extruded in two stages with an inner portion of the cable core initially extruded around the central strength member, and an outer portion of the cable core thereafter being extruded about the inner portion of the cable core. By extruding the cable core in two stages, each portion of the cable core can cure more quickly and uniformly, thereby reducing slumping.
Once the cable core has cured, optical fibers, such as ribbons of optical fibers, can be disposed within the slots defined by the cable core. An outer protective jacket can then be extruded over the cable core and the optical fibers in order to complete the fabrication of the fiber optic cable.
Fiber optic cables are generally designed to meet or exceed predetermined product specifications. Among other parameters, these specifications commonly define the weight, the tensile strength, the flexibility and the crush resistance of the fiber optic cables, with fiber optic cables that are lighter, stronger, more flexible and/or more crush resistant being generally more preferred.
While the demand for fiber optic cable continues to escalate, the demand for fiber optic cables having a large count of optical fibers, such as a thousand or more optical fibers, is especially increasing. Although fiber optic cables having large counts of optical fibers are available, these fiber optic cables oftentimes are quite heavy and somewhat inflexible. As such, the installation of these fiber optic cables having large counts of optical fibers can be somewhat cumbersome. As such, fiber optic cables, such as large count fiber optic cables, that are lighter and more flexible than conventional fiber optic cables are desired.
In view of the foregoing, a fiber optic cable product according to one aspect of the present invention includes a strength member and an elongate cable core surrounding a and mechanically coupled to the strength member such that the strength member extends lengthwise therethrough, wherein the cable core defines a plurality of lengthwise extending slots and the cable core also defines a plurality of voids proximate the strength member and disposed in a symmetrical arrangement thereabout. According to another aspect of the present invention, a fiber optic cable product includes a strength member and an elongate cable core surrounding and mechanically coupled to the strength member such that the strength member extends lengthwise therethrough, wherein the cable core defines a plurality of lengthwise extending slots and the cable core also defines a plurality of voids proximate the strength member and extending lengthwise through the cable core. According to either aspect of the present invention, the fiber optic cable product is advantageously lighter and more flexible than a conventional fiber optic cable product of the same size and construction as a result of the plurality of voids defined by the cable core.
A method for forming a fiber optic cable product is also provided according to another aspect of the present invention and includes the steps of providing a lengthwise extending strength member and extruding a cable core around the strength member such that the cable core is mechanically coupled thereto, wherein the extruding step includes the steps of defining a plurality of voids proximate the strength member and extending lengthwise through the cable core and defining a plurality of outwardly opening slots extending lengthwise along the cable core. The extrusion of the cable core can be performed in either one step in which the slots and the voids are formed concurrently, or in two steps in which an inner portion of the cable core that defines the voids can be extruded prior to extruding thereabout an outer portion of the cable core that defines the slots. Regardless of the manner in which the cable core is extruded, optical fibers can then be disposed in the slots defined by the cable core and a protective jacket can be extruded around the cable core and the optical fibers to complete the fabrication of the fiber optic cable.
An apparatus for extruding at least a portion of a cable core having an outer surface with a predetermined shape is also provided according to another aspect of the present invention and includes an extruder having an extruder die that defines a die opening that serves to shape the outer surface of the cable core and an extruder tip that cooperates with the extruder die to at least partially define an internal cavity into which molten thermoplastic material is introduced prior to being forced through the die opening, and that further includes a plurality of calibration veins that extend from the extruder tip and through at least a portion of the internal cavity of the extruder to define a plurality of voids that are internal to the cable core without opening through the outer surface of the cable core. Typically, the calibration veins serve not only to define the voids, but also to maintain the size and shape of the voids as the cable core cures, thereby avoiding distortion of the voids. In this regard, the plurality of calibration veins can extend outwardly from the internal cavity and through the die opening and/or the calibration veins can define tubular passageways through which gas can be injected into the voids defined by the cable core.